Dichromatic photomask and a method for its fabrication

Abstract

A method of manufacturing a photomask for the production of dual depth features on substrates, and the photomask so manufactured, wherein the method of manufacturing the photomask is comprised of the steps of: (1) coating a substrate which transmits at least two selected wavelengths with: a) an optical filter material which prevents the transmission of at least one of the wavelengths, b) an opaque masking material, and c) a dual tone photoresist; (2) using a single mastering tool to selectively expose areas of the coated substrate to one of the wavelengths; (3) developing the photoresist; (4) etching the exposed masking material and optical filter material; (5) exposing the remaining coated substrate; (6) developing the remaining photoresist; (7) etching the exposed surface; and (8) stripping away the remaining photoresist.

What is claimed is: 
     
       1. A process of manufacturing a photomask comprising the steps of: overlaying an electromagnetic radiation transmissive substrate with an electromagnetic radiation filter layer, the filter layer being comprised of a material which passes electromagnetic radiation of a wavelength which causes acceleration dissolution and which blocks electromagnetic radiation which causes deceleration dissolution in a dual tone photoresist process;   overlaying the filter layer with an electromagnetic radiation blocking layer such that the filter layer is located between the substrate and the blocking layer, the radiation blocking layer comprised of a material which blocks both electromagnetic radiation of a wavelength which causes acceleration dissolution and electromagnetic radiation which causes deceleration dissolution in said dual tone photoresist process;   overlaying the blocking layer with a dual tone photoresist layer, said photoresist layer having at least one dissolution accelerating additive and at least one dissolution decelerating additive;   using a mastering tool to generate electromagnetic radiation of a first wavelength and radiation of a second wavelength and exposing first areas of the photoresist layer to radiation of the first wavelength, second areas of said photoresist layer to radiation of the second wavelength, while leaving third areas of the photoresist layer unexposed to any radiation, the radiation of the first wavelength activating the dissolution decelerating additive of the photoresist layer and the radiation of the second wavelength activating the dissolution accelerating additive of the photoresist layer; and   removing the photoresist, blocking and filter layers from the second areas, removing the photoresist layer from the first areas, and removing the photoresist and blocking layers from the third areas.   
     
     
       2. The process of claim 1, wherein the step of removing the layers includes the steps of: developing the photoresist layer in the second areas;   removing the blocking and filter layers in the second areas;   exposing the photoresist layer in the first and third areas to radiation of the second wavelength;   developing the photoresist layer in the third areas;   removing the blocking layer in the third areas; and   stripping away the remaining photoresist layer.   
     
     
       3. The process of claim 1, wherein the removal of the radiation blocking and filter layers is achieved by etching. 
     
     
       4. A photomask produced by a process as described in claim 1. 
     
     
       5. A photomask produced by a process as described in claim 2. 
     
     
       6. A photomask produced by a process as described in claim 3. 
     
     
       7. A process of manufacturing optical disk substrates comprising the steps of: making a photomask comprising the steps of:   overlaying an electromagnetic radiation transmissive substrate with an electromagnetic radiation filter layer such that the filter layer is located between the substrate and the blocking layer, the filter layer being comprised of a material which passes electromagnetic radiation of a wavelength which causes acceleration dissolution and which blocks electromagnetic radiation which causes deceleration dissolution in a dual tone photoresist process;   overlaying the filter layer with an electromagnetic radiation blocking layer, the radiation blocking layer comprised of a material which blocks both electromagnetic radiation of a wavelength which causes acceleration dissolution and electromagnetic radiation which causes deceleration dissolution in said dual tone photoresist process;   overlaying the blocking layer with a dual tone photoresist layer, said photoresist layer having at least one dissolution accelerating additive and at least one dissolution decelerating additive;   using a mastering tool to generate electromagnetic radiation of a first wavelength and radiation of a second wavelength and exposing first areas of the photoresist layer to radiation of the first wavelength, second areas of said photoresist layer to radiation of the second wavelength, while leaving third areas of the photoresist layer unexposed to any radiation, the radiation of the first wavelength activating the dissolution decelerating additive of the photoresist layer and the radiation of the second wavelength activating the dissolution accelerating additive of the photoresist layer; and   removing the photoresist, blocking and filter layers from the second areas, removing the photoresist layer from the first areas, and removing the photoresist and blocking layers from the third areas;   exposing electromagnetic radiation through the photomask to an optical disk substrate coated with a photoresist layer having a dissolution accelerating additive and a dissolution decelerating additive; and   removing material from the substrate in accordance with the state of the exposed regions.   
     
     
       8. The process of claim 7, wherein the step of removing the layers includes the steps of: developing the photoresist layer in the second areas;   removing the blocking and filter layers in the second areas;   exposing the photoresist layer in the first and third areas to radiation of the second wavelength;   developing the photoresist layer in the third areas;   removing the blocking layer in the third areas; and   stripping away the remaining photoresist layer.   
     
     
       9. The process of claim 7, wherein the removal of the radiation blocking and filter layers is achieved by etching. 
     
     
       10. The process of claim 1, wherein the filter layer is comprised of a metal oxide. 
     
     
       11. The process of claim 1, wherein the filter layer is comprised of TiO 2 . 
     
     
       12. The process of claim 7, wherein the filter layer is comprised of a metal oxide. 
     
     
       13. The process of claim 7, wherein the filter layer is comprised of TiO 2 .